An example of a hybrid vehicle is disclosed in Japanese Unexamined Patent Application Publication No. 2015-131573. The hybrid vehicle includes an electric motor for driving a propelling device, and a battery for supplying electric power to the electric motor. The vehicle further includes a temperature sensor for detecting a temperature of the battery, and a vehicle control system for determining allowable output power of the battery based on the detected battery temperature and controlling discharge of the battery to prevent discharge electric power of the battery from exceeding the allowable output power.
When such a utility vehicle includes a lithium ion battery as the battery, for example, the control system determines an upper limit discharge current value based on the detected battery temperature to regulate discharge of the battery so that discharge current of the battery does not exceed the upper limit discharge current value, thereby to reduce deterioration of the battery caused by discharge.
When the battery temperature is falling, this control system gradually increases the upper limit discharge current value as the battery temperature falls so that the lower the battery temperature is, the higher the upper limit discharge current value is. However, if the battery has a high temperature and the upper limit discharge current value is intended to immediately start to increase as the battery temperature falls, the battery temperature falls less easily because the battery has already have the high temperature and further because heat generation also easily occurs in the battery with increase of the discharge current value, as result of which deterioration of the battery is prevented less easily.
On the other hand, when the battery temperature is rising, this control system gradually decreases the upper limit discharge current value as the battery temperature rises so that the higher the battery temperature is, the lower the upper limit discharge current value is. However, if the upper limit discharge current value is set to a maximum discharge current value of the battery and the upper limit discharge current value is intended to immediately start to decrease as the battery temperature rises, power to be supplied to the electric motor drops to easily reduce driving torque of the propelling device.